RE-APPRAISAL OF THE SANTA RITA GREENSTONE BELT STRATIGRAPHY, CENTRAL BRAZIL, BASED ON NEW U-PB SHRIMP AGE AND SM-ND DATA OF FELSIC METAVOLCANIC ROCKS

Resumo

The Santa Rita greenstone belt represents one of the supracrustal belts of the Archaean terranes of Goiás, central Brazil. The stratigraphic sequence of this greenstone belt comprises a lower unit made of komatiites and basalts and an upper metasedimentary unit made of carbonaceous schist, chert, iron formation and marble, unconformably overlain by clastic metasedimentary rocks. Felsic metavolcanics occur at the interface between the metabasalts and the upper metasedimentary pile. U-Pb SHRIMP age for zircons from the felsic metavolcanics reveal that it is not part of the Archaean sequence, but represents the product of a Mesoproterozoic (1580 ± 12 Ma) magmatic event. Sm-Nd isotopic data (initial e_CHUR values between -10.5 and –14.9) and T_DM values of 3.0 and 3.2 Ga, within the range of the surrounding TTG terranes, indicate that the original felsic magmas were produced by re-melting of Archaean crust. The data demonstrate that the Goiás greenstone belt contains infolded and imbricated Proterozoic rocks, as previously suggested by Sm-Nd isotopic analyses of some of the upper detrital metasedimentary rocks.